Atomic Structure Timeline

Democritus

460

Everything is made of atoms which are indivisible and indestructible. Between atoms lies empty space and atoms are always moving. He also found that there are an infinite number of atoms which are different shaped are sized.

Isaac Newton

Oct 21, 1704

Atoms were held together by attractions called forces. He adapted atomism to fit the concept of God’s role in creation.

John Dalton

Oct 21, 1803

Development of modern atomic theory. Atoms of an element were the same as its weight and that the atoms of different elements had different weights.

J.J Thompson

Oct 21, 1888

Discovery of the electron and invention of the plum pudding model which was later found to be untrue by E. Rutherford.

G.J Stoney

Oct 21, 1894

Electricity was made of electrons, but this was just a theory at the time.
Experiment: found this through information and data from the electrolysis of water and the kinetic theory of gases.

Planck

Oct 21, 1900

Established the quantum theory in which energy can only be absorbed or radiated in discrete values or quanta.

Nagaoka

Oct 21, 1903

Electrons spin around the nucleus, therefore electrostatic force is present.

Robert Milikan

Oct 21, 1909

found out the charge of an electron Experiment: Oil-drop experiment/ falling drop method.

Ernest Rutherford

Jan 1, 1911

Devised the Rutherford model, which is a model of the atom, discovery of protons and suggested the idea of neutrons in the nucleus.

H.G.J Mosley

Oct 21, 1914

Arranged the Periodic Table in order of the atomic numbers of the elements.

Niels Bohr

Oct 21, 1922

Made the Bohr model of the atom which showed that electrons moved in specific orbits and the shell model of the atom in which an element’s chemical properties are determined by the number of electrons in the outermost orbit.

James Chadwick

Oct 21, 1932

Discovered and proved that neutrons existed.